1. Field of the Invention
This invention relates to printing medium, and more specifically to medium useful for dielectric copying, printing, plotting and recording.
2. Description of the Prior Art
Methods for dielectric copying, printing, etc. are well known in the prior art. See for example, the copending patent application by Rutherford, et al. filed June 3, 1980 and assigned Ser. No. 155,937. Prior art methods for dielectric copying and printing etc., require a printing medium substrate which is through-conductive, and which contains a dielectric coating on one surface. Such a prior art dielectric recording medium is shown in FIG. 1. Prior art recording medium 99 is comprised of "through-conductive" material 100 having top surface 101 and bottom surface 102. For the purpose of this specification, a material such as material 100 is "through-conductive" when an electric current can be made to flow between top surface 101 and bottom surface 102 in response to an electrical potential applied between surfaces 101 and 102 such that the material is appropriate for use in dielectric copying machines of a type well-known in the art. Such dielectric copy machines comprise, for example, the Benson-Varian Model 9336 manufactured and sold by Benson-Varian Incorporated, 385 Ravendale Drive, Mountain View, Calif. 94043. Dielectric insulating material 105 is applied as a coating on top surface 101 of recording medium 100. Prior art dielectric recording medium used either paper or vellum as through-conductive material 100. While paper and vellum are not normally through-conductive, by applying a conductive chemical solution, the paper or vellum will absorb this chemical solution and thus become conductive. Prior art materials which can be made through-conductive are limited to paper or vellum, in that other material useful for drafting or printing purposes, such as mylar (a trademark of Dupont), polyester film, and acetate film have volume resistivities in excess of 10.sup.14 ohms-in, surface resistivities in excess of 10.sup.14 ohms/square, and are impervious to known conductive chemical solutions.
For the recording medium shown on FIG. 1, images may be printed thereon by well-known techniques. Such techniques apply an electric potential to through-conductive material 100, while passing top surface 106 of dielectric coating 105 past a recording head containing numerous styli. The styli are controlled to apply an electric charge to top surface 106 of dielectric coating material 105 at desired locations. Recording medium 100 then acts as a capacitor with points of charge stored on surface 106. A liquid toner solution containing carbon particulates is then applied to surface 106, with carbon particulates adhering to the locations on surface 106 corresponding to said stored points of charge. Surface 106 is then dried and developed, firmly affixing the carbon particles to surface 106 where points of charge had previously been stored. In this fashion, a permanent print is obtained.
One of the disadvantages with prior art dielectric recording methods is that only paper or vellum can be used, in that other common drafting or printing materials cannot be made through-conductive. Paper and vellum are much more easily damaged than other media such as mylar or acetate film and are substantially non-transparent.